The use of poppet valves in pneumatic fastener driving apparatus for controlling the application of pressurized air to the driving piston is well known, as evidenced by U.S. Pat. Nos. 4,098,171, 4,196,833, 4,227,637, and 4,339,065. Such valves typically comprise a movable valve member adapted for linear travel between pre-set limits, and a resilient sealing means on the movable valve member for making a tight seal with the piston cylinder so as to isolate the piston from the pressurized air supply. Because pneumatic fastener driving apparatus for driving fasteners into steel or concrete typically are powered by air at only about 125-150 psi, it is essential for maximum fastener driving efficiency that effective sealing be achieved between the poppet valve and piston cylinder when the poppet valve is positioned to block application of pressurized air to the piston.
Tradepersons and skilled practioners have recognized that deterioration of the resilient sealing means, as occurs with prolonged use of the pneumatic driver, reduces the effectiveness of the sealing between the poppet valve and the piston cylinder, thereby reducing the speed and power of the apparatus. Unfortunately with known designs it is generally expensive and/or time consuming to replace the poppet valve sealing means, and in some cases it is difficult if not impossible to perform the replacement in the field.